--- title: Do vaccines cause ADHD, autism, and other neurodevelopmental disorders? description: 'Navigating the debate around childhood vaccines isn’t easy. We break down the history behind the claims and what large-scale studies actually show about the safety of vaccines for kids. ' slug: childhood-vaccine-safety author: Heidi Cope, MS reviewer: Elizabeth Harstad, MD, MPH published: '2026-08-14T00:00:00.000Z' date_modified: '2026-08-14T00:00:00.000Z' thumbnail: https://cdn-images.understood.org/p0qf7j048i0q/37PexTQF7PH7QjET0Fm6BK/bedac6aad73a1cfa1e413086c5df25e6/GettyImages-1471938961.jpg source_url: https://www.understood.org/en/articles/childhood-vaccine-safety lang: en --- # Do vaccines cause ADHD, autism, and other neurodevelopmental disorders? ## Quick take - Decades of large studies, across many countries and millions of children, have found no link between vaccines and autism, ADHD, or other neurodevelopmental disorders. - The misconception traces back to a single 1998 study that was later found to be fraudulent. - Major health organizations continue to affirm vaccine safety. But vaccine hesitancy persists — partly because early signs of neurodevelopmental disorders tend to show up around the same age kids get routine vaccines. This is a coincidence in timing, not cause and effect. - Spacing out vaccines and taking them differently from the recommended schedule does not reduce neurodevelopmental disorder rates in children. The [first vaccine was developed](https://doi.org/10.1073/pnas.1400472111) more than 200 years ago, and childhood vaccination has been a [standard medical practice since the 1950s.](https://historyofvaccines.org/getting-vaccinated/vaccines-children/development-immunization-schedule/) It’s estimated that vaccines have [saved at least 154 million lives](https://www.who.int/news/item/11-12-2025-who-expert-group-s-new-analysis-reaffirms-there-is-no-link-between-vaccines-and-autism) in the past 50 years.  But with so much discussion around the safety of vaccines, you might be wondering what the research actually shows. Why do concerns about vaccines causing developmental disorders, like autism and ADHD, still come up?  We’ll take you through some of the top questions about pediatric vaccine safety and what the research actually shows.  ## Where did the idea of vaccines causing autism come from? In 1998, Dr. Andrew Wakefield and his colleagues [published a study](https://doi.org/10.1016/S0140-6736%2897%2911096-0) in a research journal called *The Lancet*. The study looked at 12 children who had stomach problems and had lost skills they’d already learned, like talking. Nine of the 12 children were also diagnosed with autism. All 12 had received the measles, mumps, and rubella (MMR) vaccine. And parents of eight of the children said symptoms started shortly after vaccination. Based on this, Wakefield suggested a possible link between the vaccine and autism — an idea that has worried parents ever since.  After the study was published, other researchers began questioning the results. The study was small and had no control group, meaning it didn’t compare the children to a similar group of unvaccinated kids. In 2010, [The Lancet retracted the paper](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2810%2960175-4/abstract) after the UK’s General Medical Council found that Wakefield did not have ethics approval for the study.  A [2011 investigation by journalist Brian Deer](https://doi.org/10.1136/bmj.c5347) (approved by *The Lancet*) went further, concluding the study was fraudulent. Deer found that Wakefield had altered the children’s medical histories to support his claim. Wakefield also had financial conflicts of interest he hadn’t disclosed — a lawyer preparing a lawsuit against MMR vaccine makers had paid him, and Wakefield had filed a patent for his own competing measles vaccine. Wakefield eventually lost his medical license for ethical violations and fraudulent claims.  ## What do follow-up studies show about the safety of vaccines for kids? Since the Wakefield study, many researchers have studied vaccination and neurodevelopmental disorders like ADHD and autism. These studies are large, often looking at hundreds of thousands of kids, unlike Wakefield’s study, which only included 12 children. The takeaways from these large studies remain the same: Vaccination does not cause neurodevelopmental disorders like autism and ADHD in kids.  Here’s what studies on common vaccines and vaccine ingredients have found:  ### MMR (measles, mumps, and rubella) vaccine The [American Academy of Pediatrics (AAP) recommends](https://www.aap.org/en/patient-care/measles/measles-vaccine/?srsltid=AfmBOooz0pGtFSY1KnocVbW3-25FgaZasncqCWC7S6bkTDYhJHXpof4M) that kids receive two doses of the MMR vaccine to protect against mumps, measles, and rubella: [one dose at 12 to 15 months and one dose at 4 to 6 years.](https://www.aap.org/en/patient-care/immunizations/aap-immunization-faq/?srsltid=AfmBOoq-mP97weLs3abhkNz31Fw8SlerBW7MwAKs3GsQfG6iDPRYcojg) This combination schedule has been tested and is recommended to prevent delays in immunity. - In 2002, [researchers in Denmark](https://doi.org/10.1056/NEJMoa021134) looked at every child born in the country over the course of seven years (1991 to 1998) — around 537,000 kids. At the time of the study, the MMR vaccine in Denmark was the same one used in the U.S., and kids in Denmark receive MMR doses at 15 months and 12 years. The researchers found no evidence that the MMR vaccine causes autism.  - In 2019, researchers in Denmark did a [follow-up study](https://doi.org/10.7326/M18-2101) of another 657,000 kids. This study found that the MMR vaccine does not raise a child’s risk of autism. That was true even for kids with other risk factors, like a family history of autism. - A [2019 review](https://doi.org/10.1002/14651858.CD004407.pub5) of 51 similar studies, looking at more than 13 million kids, and a more recent [study from 2026](https://doi.org/10.1097/INF.0000000000005349) also had the same result.  ### Tdap (tetanus, diphtheria, and pertussis) vaccine The Tdap vaccine is recommended for mothers to get during pregnancy to help protect their children from whooping cough.  - A [2020 study](https://doi.org/10.1093/aje/kwaa074) looked at more than 85,000 parent-child pairs. Researchers found no link between getting vaccinated while pregnant and ADHD in kids.  ### COVID-19 vaccine The AAP recommends the [COVID vaccine](https://www.healthychildren.org/English/health-issues/conditions/COVID-19/Pages/when-can-kids-get-the-COVID-vaccine-or-booster.aspx) for all children ages 6 months to 23 months. They also recommend it for children and teens ages 2 to 18 who have certain risk factors, like health conditions that increase their risk of severe COVID.  The COVID-19 vaccine is newer than most childhood vaccines, so it hasn’t been studied for as long. However, researchers have already started looking into whether it might affect how children’s brains develop.  - [One study](https://doi.org/10.1001/jamapediatrics.2023.5743) followed about 2,000 children whose birth parent got the vaccine during pregnancy. It found no higher risk of developmental delay by the time the children turned 18 months old.  - Researchers plan to keep following these children as they get older, and more studies are underway to better understand long-term effects of the COVID-19 vaccines.  ### Thimerosal Some parents worry about thimerosal, a mercury-based preservative used in a few vaccines. [Mercury poisoning](https://www.ncbi.nlm.nih.gov/books/NBK499935/) can cause health problems, including damage to the brain and nerves. Because of this, thimerosal has been studied closely to make sure it’s safe to use in vaccines.  - [One large review](https://doi.org/10.1016/j.neuro.2014.06.007) looked at 14 different studies on mercury exposure. It found no link between thimerosal and ADHD or autism. - It did, however, find a link between ADHD and mercury from the environment, like mercury found in some fish. Mercury from the environment is still something to watch out for. But the type and amount of mercury used in vaccines has been shown to be safe.  ## Does the number of vaccines kids take cause ADHD or autism? Some people worry that the *number *of vaccines children receive is linked to rising rates of ADHD, autism, and other neurodevelopmental disorders. But the U.S. isn’t unusual in how many [vaccines it recommends.](https://www.aap.org/en/news-room/news-releases/aap/2026/american-academy-of-pediatric-issues-recommended-childhood-and-adolescent-immunization-schedule-for-2026)  The American Academy of Pediatrics recommends immunization against 18 infectious diseases for children and adolescents. It’s recommended that children under the age of 6 be immunized against [12 of these diseases.](https://downloads.aap.org/AAP/PDF/AAP-Immunization-Schedule.pdf) That’s because many of them are more dangerous for young kids if they were to get sick. And vaccinating at a young age also builds immunity before exposure to these diseases.  While it may seem like a large number, protection from several diseases can be combined in one shot. For example, three diseases — measles, mumps, and rubella — are covered by the MMR vaccine.  [Germany and South Korea recommend](https://www.rki.de/EN/Topics/Infectious-diseases/Immunisation/STIKO/STIKO-recommendations/Downloads/04_25_english.pdf?__blob=publicationFile&v=3) that children under the age of 6 get vaccinated against a similar number of diseases. In [South Korea,](https://www.kdca.go.kr/eng/4408/subview.do) some shots may protect children against five diseases at once.  Diagnosed rates of autism and ADHD vary from country to country, but this mostly reflects differences in [how each country screens and diagnoses](https://publications.aap.org/aapnews/news/31909/CDC-report-Autism-rate-rises-to-1-in-31-children) these conditions, not the number of vaccines children receive.  It’s also important to note that the total number of vaccine shots a child receives depends on which formulation is available. And choosing combination vaccines, like the MMR vaccine, can have [several benefits:](https://drive.google.com/file/d/1SOGCVatFf-UXid_K2kHKqPd7Dt9OUzmo/view) - Reduces overall rate of adverse events compared to giving individual shots  - Reduces discomfort in kids from receiving the shot  - Limits the number of visits to the pediatrician  - Lowers health care costs to the parents for those visits  - Gets kids protected from disease and serious illness earlier  Researchers have also [studied vaccine schedules,](https://doi.org/10.1542/peds.2009-2489) following children in the U.S. who received vaccines according to the recommended immunization schedule in their first year to see the outcome at ages 7 to 10 years..  - These researchers tested kids’ executive function and reasoning skills and assessed them for hyperactivity and inattention.  - They found no differences between children who were vaccinated on schedule compared to those whose vaccinations were delayed or who were unvaccinated.  Scheduling childhood vaccinations as recommended by your pediatrician will not increase your child’s risk of having a neurodevelopmental disorder. And spacing out vaccines can cause a delay in full immunization against childhood diseases — putting your child at greater risk for serious illness.  ## What do major health organizations say about childhood vaccine safety? The Global Advisory Committee on Vaccine Safety at the World Health Organization (WHO) continues to check childhood vaccines for safety. In 2025, they looked again at [vaccines and autism risk.](https://www.who.int/news/item/11-12-2025-statement-gacvs-vaccines-autism) Thirty-one studies were reviewed and WHO reaffirmed that [vaccines do not increase autism risk.](https://www.who.int/news/item/11-12-2025-who-expert-group-s-new-analysis-reaffirms-there-is-no-link-between-vaccines-and-autism)  The AAP publishes vaccine schedule recommendations for children in the United States. In a [recent statement,](https://www.aap.org/en/news-room/news-releases/aap/2026/aap-statement-in-response-to-executive-order-on-vaccines/) the AAP shared that “vaccine recommendations from the AAP are tailored to the health of children living in the United States and are based on decades of research and systematic tracking of real-world experiences.” The AAP continues to check new studies and confirm that vaccines do not cause neurodevelopmental disorders in children. Here are some helpful resources:  - [A brief guide on how childhood vaccines are developed, tested, and approved](https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/how-vaccines-are-developed-tested-for-safety-and-approved-step-by-step.aspx) - [Evidence that the AAP uses to make vaccine schedule decisions](https://www.healthychildren.org/English/safety-prevention/immunizations/Pages/vaccine-studies-examine-the-evidence.aspx) In late 2025, the Centers for Disease Control and Prevention (CDC) changed the [wording on its website.](https://www.cdc.gov/vaccine-safety/about/autism.html) It used to say that vaccines do not cause autism, but now it says that the claim cannot be fully proven. This change goes against the findings from decades of large studies, as well as the current position of many independent health organizations.  ## Why do misconceptions still exist? ADHD and autism are both neurodevelopmental disorders that are likely caused — in part — by [genetics](https://www.understood.org/en/articles/what-causes-adhd). Both conditions often [run in families and are related to each other](https://www.understood.org/en/articles/ive-heard-that-autism-and-adhd-are-related-is-that-true). For instance, if you have ADHD, it’s likely that you have a relative with either ADHD or autism.  So why are some people still concerned about vaccines causing ADHD or autism?  Part of it has to do with a timing coincidence. Parents might first see signs of developmental disorders like ADHD or autism around the time of childhood vaccinations. For example, the MMR vaccine is typically given to a 12- to 18-month-old. That’s the [same time frame](https://www.healthychildren.org/English/health-issues/conditions/Autism/Pages/Early-Signs-of-Autism-Spectrum-Disorders.aspx) parents may start to notice signs of autism in their child. [ADHD is typically diagnosed starting at age 4,](https://doi.org/10.1542/peds.2019-2528) but signs may show up earlier in some kids.  Social media also shapes how people get health information. Even though [vaccine safety has been studied](https://doi.org/10.1177/13623613251345281) so thoroughly, misleading claims spread easily online. Social media messages that contain misinformation about vaccines typically have [higher engagement rates,](https://doi.org/10.2196/54657) making them more likely to “go viral.” And those types of messages make an impact.  In recent polling conducted by KFF: - 61 percent of parents said they’ve encountered [misinformation about vaccines](https://www.kff.org/health-information-trust/kff-tracking-poll-on-health-information-and-trust-the-publics-views-on-measles-outbreaks-and-misinformation/) causing autism on social media.  - 37 percent of adults who use social media believe “the myth that the MMR vaccine leads to autism” — nearly double the rate of adults who don’t use [social media for health information.](https://www.ajmc.com/view/provider-trust-social-media-use-can-shape-vaccine-myth-belief)  ## What to do if you have more vaccine questions It’s always a good idea to talk through any potential side effects with your child’s pediatrician. After all, like any medical procedure, vaccines do carry minor risks and potential side effects. For example, the [MMRV (measles, mumps, rubella, and varicella) vaccine](https://doi.org/10.1002/14651858.CD004407.pub5) can raise the risk of febrile seizures (short seizures caused by a high fever that are usually harmless). But your [child’s chance](https://www.aap.org/en/news-room/fact-checked/fact-checked-febrile-seizures-do-not-cause-brain-damage-or-long-term-health-effects/) of having a febrile seizure from this vaccine is *lower *than their overall chance of having one in childhood due to a viral infection.  Wanting to understand what’s going into your child’s body is a good instinct. Researchers have spent decades making sure that childhood vaccines remain safe and effective at preventing serious illness.  If you still have questions or concerns, your pediatrician or primary care provider can help answer your questions about childhood immunizations. Having an open and honest conversation with them about your concerns can help you make more informed decisions about your child’s health. *Thumbnail image credit: FatCamera via Getty Images. * --- ## Explore related topics and articles - [The difference between ADHD and autism](https://www.understood.org/en/articles/the-difference-between-adhd-and-autism) - [ADHD symptoms at different ages](https://www.understood.org/en/articles/signs-of-adhd-at-different-ages) - [I’ve heard that autism and ADHD are related. Is that true?](https://www.understood.org/en/articles/ive-heard-that-autism-and-adhd-are-related-is-that-true) --- ```json [{"@context":"https://schema.org","@type":"WebPage","@id":"https://www.understood.org/en/articles/childhood-vaccine-safety#webpage","url":"https://www.understood.org/en/articles/childhood-vaccine-safety","description":"Navigating the debate around childhood vaccines isn’t easy. 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